It is well known that when an electrical circuit is broken, there is a tendency for a spark to occur. Many fires have been ignited unintentionally by an electrical spark occurring in an explosive atmosphere. That is, if the atmosphere in the vicinity of the spark should include more than a critical amount of explosive gases or vapors, an explosive and fire may result and possibly cause extensive damage or loss of life. Accordingly, precautions are customarily taken with electrical circuits in locations where an explosive atmosphere exists, or might exist. An explosion or a fire, once started, may travel through an electrical conduit, and/or an explosive atmosphere may enter an electrical conduit and be guided to a location where a spark might be generated. Accordingly, to avoid such transmission through conduits, it has become conventional, under selected circumstances, to provide barriers within the conduit. Examples of structures which provide barriers may be seen in U.S. Pat. Nos. 2,711,438; 2,835,722 and 4,216,349, issued June 21, 1955, to C. H. Bissell, May 20, 1958, to Arthur I. Appleton and Aug. 5, 1980 to Eigil Wium, respectively. As may be seen in these structures, a special fitting is used to join two sections of conduit, and a sealing compound is placed within a well, or chamber, in the fitting to provide a barrier.
Even in locations which are presumed to be dry it is not uncommon for water to form in the interior of the conduit. This is normally a result of a combination of the changes in atmospheric conditions, humidity, and/or temperature. As a result, outside air is drawn into the conduit system as it "breathes". If such air carries sufficient moisture, it may condense within the system when the temperature decreases and chills the air. The resultant water accumulation will remain within the conduit and more will be added thereto in response to repeated breathing cycles. A collection of such water can adversely affect the electrical circuit, and/or corrode the inferior of the conduit. Therefore, it has been found desirable to make a provision for draining water, or other liquids, that might otherwise collect in the sealed fitting. A simple opening to effect a drain would, obviously, defeat the purpose of the seal. Suitable drains have been devised which will permit the drainage of liquid from a sealed enclosure without adversely affecting the effectiveness of the seal for preventing the transmission of fire, explosions and/or explosive atmospheres. One form of suitable seal is disclosed in U.S. Pat. No. 2,405,927, issued Aug. 13, 1946, to N. A. Tornblom. A wide variety of drains for different types of applications have been developed. The drain, per se, does not form an integral part of this invention, except to the extent that the fitting must allow for the inclusion of one of the variety of drains available. Accordingly, it is believed that the disclosure of the details of any specific drain would only unnecessarily enlarge this specification and obscure the inventive concept.
Typical fittings, of the class described, usually include four ports, two of which provide means for coupling the fitting to conduit. Another port provides a means for connecting a suitable drain plug, and the last port provides a working access for the application of a suitable sealing compound within a well, or chamber, in the fitting. After the application of the sealing compound, a plug closes that access port. In typical prior art structures, care had to be exercised to avoid allowing the sealing compound to seal off the drain port. In some structures, a drain port plug was provided and removed after the hardening of the sealing compound. In other structures, a drain port plug and/or core was provided.
In some structures such plug or core was placed or removed through the access or working port and therefore sometimes inconvenienced the artisans working on the fitting and preparing it for receipt of the filling compound. The plug or core also tended to obscure vision, making it difficult to see inside the fitting and determine if the level of the sealing compound in the chamber was at an appropriate level. As a result, it was not unusual to have fittings with either over or underfill.
The structure disclosed in the last named patent obviated the need for a drain port plug or core; and, therefore, had no such device projecting into the working port to obstruct vision or working space. A feature of that structure resided in the fact that the upper limit of the drain port and the desired level of the sealing compound are coplanar. Accordingly, when liquid sealing compound was poured into the fitting through the working port, excess sealing compound could not remain within the fitting as it would overflow through the drain port. Another feature resided in the fact that the working port had no direct in-line communication with the drain port. Therefore, as sealing compound was poured into the fitting, it could not enter the drain port directly but had to flow into the sealing chamber. Accordingly, the artisan preparing the connection could pour sealing compound into the fitting through the working port until such time as an overflow came out through the drain port. The presence of overflow emerging from the drain port was evidence that there was not an underfill; and, because of the coplanar level of the upper limit of the drain port and the sealing chamber, there could be no overfill. When desired, a plug with a through passage could be placed in the drain port from the lower side to protect the threads of the drain port from contact with the sealing compound.
The fitting of U.S. Pat. No. 4,216,349 serves admirably when placed in a vertical position. However, the sealing material will not have a uniform depth when the fitting is used in a non-vertical position and cannot be used in a horizontal position. Further, the fitting of the cited patent is complex and specialized and therefore, relatively costly.